The gums will become black for the following reasons: 1, long-term smoking, tea, coffee, etc., will cause tobacco stains, tea stains, coffee stains, etc. attached to the edge of the gums, making the soft tissue black. 2, poor oral hygiene environment, long-term accumulation of food debris and soft scale in the neck of the teeth will mineralize to form calculus, stimulate the gums bleeding after the calculus becomes black. 3, the use of metal porcelain full crown restoration, metal ions are easy to contact with the gums 4.The accumulation of heavy metals in the body is too high when the gums become dark or black.